Cathode ray oscillograph



May 10, 1938. H. M. DOWSETT El AL 2,116,671

CATHODE my OSCILLOGRAPH Filed Nov. 22, 1935 22 l l ll l l l Patented May10, 1938 carnonn RAY OSCILLOGRAPH Winchmore Hill, London,

Harry Melville Dowsett,

England, and Robert Cadzow,

Ardentinny,

Scotland, assignors to Radio Corporation of America, a corporation ofDelaware Application November 22, 1935, Serial No. 51,038 In GreatBritain October 26, 1934 8 Claims.

This invention relates to television and like cathode ray tubeoscillograph arrangements and more particularly to television receiversof the cathode ray tube type.

t: The most generally used and widely known cathode ray tube receiversare those wherein the intensity of the cathode ray beam is modulated independence upon received picture signals, for example, by applyingpotentials corresponding to the said received signals to a Wehneltcylinder or similar electrode in the picture reproducing tube. Variouspractical difliculties are met with in apparatus of this kind among thembeing the important difficulties that the position of the spot caused bythe incidence of the cathode ray beam upon the screen of the tube is notcompletely independent of the signal potentials applied to modulate thecathode ray beam intensity while the size of the said spot is also notcompletely no independent of such potentials. The greater the amplitudesof the picture signals the more serious do these two difficulties becomeand quite appreciable distortion occurs in many known systems by reasonof so-called spot shift and alterations in the spot size concomitantwith and due to applied potentials which are desired only to control theintensity of the spot. A fiuther difliculty which arises in usual knowncathode ray receivers is that there is a more or less pronouncedtendency for loss of high frequencies; that is to say, the highfrequency picture signals do not produce as much variation in spotintensity as they should do.

The principal object of the present invention is to provide an improvedtelevision receiver and like cathode ray tube oscillograph apparatuswherein the above mentioned disadvantages are reduced or eliminated.

According to this invention picture or other signals intended tomodulate the intensity of the cathode ray beam in a cathode ray tubereproducer are applied simultaneously and substantially in phaseopposition to at least two different electrodes of the tube and therelative amplitudes at which the signals are so applied are so chosenthat variation of spot size or spot shift due to the application ofsignal potentials to one of the two said electrodes is counterbalancedor approximately counterbalanced by reason of the application of signalpotentials to the other of said two electrodes. In general in carryingout this invention received picture signals are applied simultaneouslyand in phase opposition to the cathode of a cathode ray tube and to theWehnelt cylinder or'equivalent electrode thereof and the amplitudes atwhich these potentials are applied are so chosen that the electrostaticrelationship between the anode and cathode is substantially constantover a wide range of applied signal voltages. Accordingly in effect theinvention provides combined anode and Wehnelt cylinder modulation or inother words it provides for automatically re-adjusting the focus of thespot in such manner as to correct for any change of potential across theelectron gun due to the application of a signal voltage this beingeffected by applying a signal voltage in opposite phase to the Wehneltcylinder so that the voltage relationship between anode cathode andWehnelt cylinder remains substantially constant.

The invention is illustrated in the accompanying drawing which showsdiagrammatically one way of carrying out the said invention.

Referring to the drawing a, cathode ray tube I of the usual typecomprising a cathode 2 a Wehnelt cylinder 3 an apertured anode 4, twomutually perpendicular pairs of deflecting plates and a fluorescentscreen at the end of the tube is employed. The tube I is shown only inpart, the deflecting plates and fluorescent screen (which are as wellknown per se) being omitted from the drawing. Received picture signalsare applied through a condenser 5 across the end of a potentiometerresistance 6 one terminal of which is earthed and an adjustable tappingpoint 1 upon this potentiometer resistance is connected to the controlgrid 8 of a first amplifier valve 9. The potentiometer 6, I, constitutesthus the main or input potentiometer of the whole arrangement. Thecathode IQ of the valve 9 is in practice preferably earthed through abiasing resistance shunted by a b-y-pass condenser but these componentsare omitted from the drawing, grid bias arrangements being, for the sakeof simplicity, not shown. The anode I I of the valve 9 is connected to apositive terminal l2 of a source of anode potential (not shown) throughan anode resistance I3 in series with a decoupling resistance It and thejunction point of these two resistances is connected to earth through adecoupling condenser I5. The anode I I is also connected through acondenser It to one junction point of two parallel connectedpotentiometer resistances Il, I8, the junction point at the other endsof those resistances being earthed. A tapping point I9 upon resistanceI! is connected through a condenser 20 to one end of the filament 2 ofthe cathode ray tube (assuming the tube to have a directly heatedcathode) and also to one end of a resistance 2| whose other end isconnected to the negative terminal of a source 22 of potential. The tubecathode 2 is also connected through a source of negative bias potential(which may be adjustable if desired) in series with a bias resistance 23to the Wehnelt cylinder 3 of the cathode ray tube. In the circuitillustrated adjustable bias is obtained by the battery-potentiometercombination 24-25. The positive terminal of the source 22 is connectedto the anode 4 of the cathode ray tube and the said source of potentialis preferably shunted by a by-pass condenser (not shown). The cathode ofthe cathode ray tube if of the directly heated type, has the usualcathode heating circuit consisting of a source 26 of potential in serieswith an adjustable resistance (not shown). An adjustable tapping point21 upon the resistance I8 is connected to the grid 28 of a second valve29 which acts as a phase reversing valve the cathode 30 of this valvebeing earthed preferably through a bias resistance shunted by a by-passcondenser. For the sake of simplicity a directly earthed cathode isshown for the valve 29 as in the case of the Valve 9. The anode 3| ofvalve 29 is connected through a condenser 32 to the Wehnelt cylinder 3of the cathode ray tube and the anode 4 of the cathode ray tube isearthed. The anode 3| of the phase reversing valve 29 is also connectedto one end of an inductance 33 whose other end is connected through adecoupling resistance 34 to the positive terminal I2 of the source ofanode potential a tapping point 35 upon the resistance 34 being earthedthrough a decoupling condenser 36.

It will be appreciated that the two parallel connected potentiometersI'|l9 and l8--2'l control the potentials applied to the tube cathode 2and to the Wehnelt cylinder 3 and in operation these two potentiometersare so adjusted that errors in spot size or position due to theapplication of signals to the cathode of the cathode ray tube arecompensated or substantially compensated by reason of the application ofpicttu'e signals in opposite phase to the Wehnelt cylinder. These twopotentiometers may, if desired, be unicontrolled, that is to say, theymay be operated by a single shaft which varies them in oppositedirections so that a balance arrangement is obtained. After thesepotentiometers have been adjusted they are left in their adjustedpositions and the extent of the cathode ray beam intensity modulationcan be adjusted by controlling the input potentiometer 6-l. Theinductance 33 which is preferably air cored, produces a peaking-upeffect as regards the high frequencies and a measure of control of thepeaking-up efiect is obtainable by adjusting the tapping point 35. Suchcontrol can also be obtained by making the inductance 33 variableinstead (or as well).

Having now particularly described and ascertained the nature of our saidinvention and in what manner the same is to be performed we declare thatwhat we claim is:

1. In a cathode ray apparatus, means for amplifying input signals, acathode ray tube including anode, cathode and modulating electrodes,means for impressing a portion of said amplified signal upon the cathodeof said tube so as to change the potential of the cathode with respectto a reference potential, and means for impressing another portion ofsaid amplified signal upon a modulating electrode of the cathode raytube in opposite phase to that portion impressed upon the cathode of thetube so as to change its potential with respect to the same referencepotential, whereby shifting of the cathode ray beam and variations incross-section area of the beam due to variation in amplitude of saidinput signals are substantially neutralized and the electrostaticrelationship between the anode, cathode and modulating electrodes ismaintained substantially constant.

2. In a cathode ray apparatus, means for amplifying input signals, acathode ray tube including anode, cathode and modulating electrodes, areference potential, means for impressing a portion of said amplifiedsignal upon the cathode of said tube so as to change its potential withrespect to the reference potential in accordance with variations of thesignal, means for impressing another portion of said amplified signalupon a modulating electrode of the cathode ray tube in opposite phase tothat portion impressed upon the cathode of the tube so as to change itspotential with respect to the reference potential in accordance withvariations of the signal, and adjustable means for biasing saidmodulating electrode with respect to the cathode of the cathode ray tubewhereby the electrostatic relationship between the anode, cathode andmodulating electrodes is maintained substantially constant.

. 3. In a cathode ray apparatus, amplifying means, variable means forimpressing input signals onto the input of one of said amplifying means,a cathode ray tube including anode, cathode and modulating electrodes, areference potential, variable means for impressing a portion of theamplified input upon the cathode of the oathode ray tube so as to changeits potential in accordance with changes of the input signal withrespect to the reference potential, a phase reversing tube, variablemeans for impressing a portion of the amplified input signal onto acontrol electrode of the phase reversing tube, and means for impressinga portion of the output of the phase reversing tube onto a modulatingelectrode of the cathode ray tube whereby the electrostatic relationshipbetween the anode, cathode and modulating electrodes is maintainedsubstantially constant.

4. In a cathode ray apparatus, amplifying means, variable means forimpressing input signals onto the input of one of said amplifying means,a cathode ray tube including anode, cathode and modulating electrodes, areference potential, variable means for impressing a portion of theamplified input upon the cathode of the oathode ray tube so as to changeits potential in accordance with changes of the input signal withrespect to the reference potential, a phase re- Versing tube, variablemeans for impressing a portion of the amplified input signal onto acontrol electrode of the phase reversing tube, means for impressing aportion of the output of the phase reversing tube onto a modulatingelectrode of the cathode ray tube, and adjustable means for biasing saidmodulating electrode with respect to the cathode of the cathode ray tubewhereby the electrostatic relationship between the anode, cathode andmodulating electrodes is maintained substantially constant.

5. In a cathode ray apparatus, amplifying means, variable means forimpressing input signals onto the input of one of said amplifying means,a cathode ray tube including anode, cathode and modulating electrodes, areference potential, variable means for impressing a portion of theamplified input upon the cathode of the oathode ray tube so as to changeits potential in accordance with changes of the input signal withrespect to the reference potential, a phase reversing tube, variablemeans for impressing a portion of the amplified input signal onto acontrol electrode of the phase reversing tube, said aforementionedvariable means being uni-controlled, and means for impressing a portionof the output of the phase reversing tube onto a modulating electrode ofthe cathode ray tube whereby the electrostatic relationship between theanode, cathode and modulating electrodes is maintained substantiallyconstant.

6. In a cathode ray apparatus, means for receiving A. C. signals, acathode ray tube including cathode, anode and modulating electrodes, areference potential, means for impressing a portion of said signals ontothe modulating electrode of the cathode ray tube so as to change thepotential of said electrode with respect to the reference potential inaccordance with variations in the input signals, and means forimpressing another portion of said received signals onto the cathode ofthe cathode ray tube in opposite phase to those impressed on themodulating electrode wherebi the potential of the electrode is varied inaccordance with variations in the input signal with respect to thereference potential and whereby shifting of the cathode ray beam andvariations in cross-section area of the beam due to variations inamplitude of said input signal are substantially neutralized.

'7. In a cathode ray apparatus, means for receiving A. C. signals, acathode ray tube including cathode, anode and modulating electrodes, areference potential, means for impressing a portion of said signals ontothe modulating electrode of the cathode ray tube so as to change thepotential of said electrode with respect to the reference potential inaccordance with variations in the input signals, means for impressinganother portion of said received signals onto the cathode of the cathoderay tube in opposite phase to those impressed on the modulatingelectrode whereby the potential of said electrode is varied inaccordance with variations in the input signal with respect to thereference potential, and variable means for controlling the frequencyresponse of said cathode ray tube.

8. In a cathode ray system wherein the cross sectional area of thecathode ray beam in the tube is distorted and said beam is deflected dueto variations in the input signals to said tube, the method ofcorrecting for said aforementioned distortion which comprises the stepsof developing potentials of a like frequency but of opposing phase fromsaid input signals, and maintaining the electrostatic relationshipbetween the electrodes of the tube substantially constant by means ofsaid oppositely phased developed potentials.

HARRY MELVILLE DOWSETT. ROBERT CADZOW.

